O mundo ainda está enfrentando uma crise financeira, que começou em meados de 2007 e até o momento está longe de ser resolvida. Os mercados de ações ao redor do mundo reagiram mal e as notícias em tempo real nunca desempenharam um papel tão importante para os investidores, como visto nesta crise. Em outras palavras, o impacto dos meios de comunicação aprofundou a dinâmica de baixa dos mercados financeiros, o que é amplificada pela volatilidade intrínseca do mesmo. Assim, a Neuroeconomia veio como um novo campo de questionamentos, o qual tem a finalidade de estudar a tomada de decisão, tendo em conta o papel desempenhado pela emoção e seus aspectos fisio-patológicos. Se utiliza neste estudo uma amostra de oitenta (80) pessoas, classificados em quarenta alunos de graduação e quarenta (40) trabalhadores experientes do mercado financeiro (traders), ambos igualmente divididos em 50% do sexo masculino e 50% do sexo feminino. O escopo é de avaliar o envolvimento de uma ampla rede de circuitos neurais envolvidos na avaliação de riscos, benefícios e conflitos (esta ponderação está intimamente relacionada à serotonina em caso de riscos e benefícios no caso de dopamina) para cada grupo a fim de verificar como reagem neste ambiente. Compreender a funcionalidade de tais sistemas é de fundamental importância para a compreensão da dinâmica do mercado financeiro e de suas anomalias, ou seja, para registrar a percepção de cada indivíduo em relação ao sentimento geral do mercado, seja ele a favor ou adverso. Portanto, o principal objetivo desta tese é mapear a atividade cerebral usando uma técnica desenvolvida por Rocha (2001, 2004 e 2010), operando uma simulação de negociação da Bolsa de Valores BMF&Bovespa, a fim de compreender melhor a neurodinâmica do processo de decisão no mercado de capitais / The world is still facing a financial crisis, which started in mid 2007 and up to now is far from being solved. Stock markets around the world reacted badly and the real time news has never played such an important role to investors as seen in previous crisis. In other words, the impact of the media deepened the bear dynamics of the markets, that is, it amplified the volatility of it. Thus, Neuroeconomics comes as a new field of inquiring that has the purpose of studying decision making taking into consideration the role played by emotion and its physio-pathological aspects. Here, it is used a sample of eighty (80) volunteers, sorted out into forty undergraduate students and forty (40) experienced financial market practioneers (namely traders), both equally divided into 50% male and 50% female. The scope is to evaluate the involvement of a wide network of neural circuits involved in risk assessments, benefits and conflicts (this weighting is closely related to the serotonin neural circuits in the event of risks and benefits in the case of dopamine) so as to verify how both groups react to this environment. Understanding the functionality of such systems is of fundamental importance for understanding the dynamics of the financial market and its anomalies, ie to record the perception of each individual in relation to the general market sentiment, being it in favour or on the contrary, adverse. Therefore, the main objective of this thesis is then to map brain activity using a technique developed by Rocha et al (2001, 2004 and 2010), operating a simulation of trading within the BMF&Bovespa, in order to better understand the process of neurodynamics decision making in the capital market

This thesis documents a series of experiments designed to investigate the mechanisms subserving sub-second duration processing in humans. Firstly, duration aftereffects were generated by adapting to consistent duration information. If duration aftereffects represent encoding by neurons selective for both stimulus duration and non-temporal stimulus features, adapt-test changes in these features should prevent duration aftereffect generation. Stimulus characteristics were chosen which selectively target differing stages of the visual processing hierarchy. The duration aftereffect showed robust interocular transfer and could be generated using a stimulus whose duration was defined by stimuli invisible to monocular mechanisms, ruling out a pre-cortical locus. The aftereffects transferred across luminance-defined visual orientation and facial identity. Conversely, the duration encoding mechanism was selective for changes in the contrast-defined envelope size of a Gabor and showed broad spatial selectivity which scaled proportionally with adapting stimulus size. These findings are consistent with a second stage visual spatial mechanism that pools input across proportionally smaller, spatially abutting filters. A final series of experiments investigated the pattern of interaction between concurrently presented cross-modal durations. When duration discrepancies were small, multisensory judgements were biased towards the modality with higher precision. However, when duration discrepancies were large, perceived duration was compressed by both longer and shorter durations from the opposite modality, irrespective of unimodal temporal reliability. Taken together, these experiments provide support for a duration encoding mechanism that is tied to mid-level visual spatial processing. Following this localised encoding, supramodal mechanisms then dictate the combination of duration information across the senses.

The past twenty years have seen a successful formalization of the idea that perception is a form of probabilistic inference. Bayesian Decision Theory (BDT) provides a neat mathematical framework for describing how an ideal observer and actor should interpret incoming sensory stimuli and act in the face of uncertainty. The predictions of BDT, however, crucially depend on the observer’s internal models, represented in the Bayesian framework by priors, likelihoods, and the loss function. Arguably, only in the simplest scenarios (e.g., with a few Gaussian variables) we can expect a real observer’s internal representations to perfectly match the true statistics of the task at hand, and to conform to exact Bayesian computations, but how humans systematically deviate from BDT in more complex cases is yet to be understood. In this thesis we theoretically and experimentally investigate how people represent and perform probabilistic inference with complex (beyond Gaussian) one-dimensional distributions of stimuli in the context of sensorimotor decision making. The goal is to reconstruct the observers’ internal representations and details of their decision-making process from the behavioural data – by employing Bayesian inference to uncover properties of a system, the ideal observer, that is believed to perform Bayesian inference itself. This “inverse problem” is not unique: in principle, distinct Bayesian observer models can produce very similar behaviours. We circumvented this issue by means of experimental constraints and independent validation of the results. To understand how people represent complex distributions of stimuli in the specific domain of time perception, we conducted a series of psychophysical experiments where participants were asked to reproduce the time interval between a mouse click and a flash, drawn from a session-dependent distribution of intervals. We found that participants could learn smooth approximations of the non-Gaussian experimental distributions, but seemed to have trouble with learning some complex statistical features such as bimodality. To investigate whether this difficulty arose from learning complex distributions or computing with them, we conducted a target estimation experiment in which “priors” where explicitly displayed on screen and therefore did not need to be learnt. Lack of difference in performance between the Gaussian and bimodal conditions in this task suggests that acquiring a bimodal prior, rather than computing with it, is the major difficulty. Model comparison on a large number of Bayesian observer models, representing different assumptions about the noise sources and details of the decision process, revealed a further source of variability in decision making that was modelled as a “stochastic posterior”. Finally, prompted by a secondary finding of the previous experiment, we tested the effect of decision uncertainty on the capacity of the participants to correct for added perturbations in the visual feedback in a centre of mass estimation task. Participants almost completely compensated for the injected error in low uncertainty trials, but only partially so in the high uncertainty ones, even when allowed sufficient time to adjust their response. Surprisingly, though, their overall performance was not significantly affected. This finding is consistent with the behaviour of a Bayesian observer with an additional term in the loss function that represents “effort” – a component of optimal control usually thought to be negligible in sensorimotor estimation tasks. Together, these studies provide new insight into the capacity and limitations people have in learning and performing probabilistic inference with distributions beyond Gaussian. This work also introduces several tools and techniques that can help in the systematic exploration of suboptimal behaviour. Developing a language to describe suboptimality, mismatching representations and approximate inference, as opposed to optimality and exact inference, is a fundamental step to link behavioural studies to actual neural computations.

Made available in DSpace on 2014-06-11T19:30:53Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-04-06Bitstream added on 2014-06-13T19:19:36Z : No. of bitstreams: 1 paula_ai_dr_rcla.pdf: 1264548 bytes, checksum: f5f07951ceae1ba51d882db3847be6b2 (MD5) / A imagem corporal refere-se a experiências humanas incorporadas ao longo da vida sobre seu próprio corpo. É um construto multifacetado que une a percepção e as atitudes das pessoas, especialmente as preocupações e atitudes relacionadas à aparência física (Cash, Maikkula & Yamamiya, 2004). Quando distorcida, a representação da imagem corporal pode levar o indivíduo a riscos, tais como transtornos alimentares e depressão (Smolak, 2002), que estão entre os principais e mais sérios problemas clínicos encontrados em meninas adolescentes e mulheres jovens na atualidade (Shroff & Thompson, 2006). O objetivo geral deste estudo foi avaliar aspectos comportamentais e perceptivos da imagem corporal de meninas adolescentes com distúrbio de imagem corporal (GCD) e sem distúrbio de imagem corporal (GSD). Especificamente identificar se parâmetros comportamentais (i.e., nível de satisfação com o próprio corpo) são distintos entre os grupos; verificar em tarefa com silhuetas e em tarefa com imagens do próprio corpo a consistência dos sub-componentes afetivo, cognitivo e perceptivo de ambos os grupos; avaliar se parâmetros perceptivos (i.e., expoente da função psicofísica de potência e magnitude do erro no julgamento de dimensões do próprio corpo) diferem entre os grupos; verificar se parâmetros perceptivos são diferentes entre tarefas que incluem imagens da própria pessoa, de pessoa desconhecida e de estímulo neutro (i.e., projeção frontal de um cubo) e se estas possíveis diferenças ocorrem para ambos os grupos; se fatores como distúrbio de imagem, transtorno alimentar e IMC predizem o nível de insatisfação do próprio corpo e se predizem a magnitude do erro no julgamento de dimensões do próprio corpo. Para tanto, 43 participantes do GSD e 10 participantes do GCD responderam a testes e inventários (BSQ, EAT, escala de silhuetas e escala da imagem própria)... / Body image is a multi-dimensional construct that combines perceptions and attitudes about the body, particularly those that relate to physical appearance (Cash, Maikkula & Yamamiya, 2004). When body image perception is disturbed—most common amongst teenage girls (Shroff & Thompson, 2006), serious health risks may result, which include eating disorders and depression (Smolak, 2002). The purpose of this study was to assess the behavioral and perceptual aspects of body image in adolescent females with and without body image distortion, (BID) and (NBI). Specifically, it was to identify whether or not behavioral parameters are distinct between groups. The study attempted to verify, in both groups, levels of consistency in sub-components: affective, cognitive and perceptual, using tasks that portrayed the individual’s own body as well as a stranger’s body. Also assessed was whether or not perceptual parameters could it be determined, and whether or not perceptual parameters are different for tasks that include an individual’s own body image versus those tasks that include a stranger’s body image and a task with a neutral image. If differences existed between groups, the study attempted to assess whether or not body image disturbance, presence of eating disorder and BMI-body mass index (IMC) predicted levels of individual body dissatisfaction and magnitude of error when the individuals judged the dimensions of their own bodies. Forty-three participants comprised the NBI group, and ten participants comprised the BID group. In order to establish the behavioral components of body image, individuals in both groups were asked to complete questionnaires and inventories (BSQ, EAT, silhouette scale, SIL, and own body image scale, OBI). Also, psychophysical tasks were used to assess the perceptual components of body image. Results of the behavioral aspects related to body image showed that... (Complete abstract click electronic access below)

Orientador: Lauro Frederico Barbosa da Silveira / Banca: Adolpho Menezes de Mello / Banca: Alfredo Pereira Júnior / Resumo: O presente trabalho propõe uma discussão a respeito da fisiologia do músculo esquelético humano como um processo de caráter sígnico. Trata-se de uma abordagem interdisciplinar para se estudar as relações biológicas baseada no pensamento de Charles S. Peirce. Diferente das aproximações mecanicistas e reducionistas, que entendem o ser vivo como uma máquina cartesiana, a tendência semiótica busca uma abordagem mais ampla sobre as fundações da biologia, liberando o pensamento e lançando nova luz nas investigações dos seres vivos. Tal estudo poderá contribuir no entendimento das relações psicofísicas do corpo por considerar os músculos uma ampla esfera de processos mentais. Este texto inicia-se com uma discussão a respeito da natureza da conduta muscular. Na segunda parte do texto, examinar-se-á a conduta muscular como um hábito baseado na experiência. Na terceira parte, a relação entre causação final e eficiente na conduta muscular será examinada a seguir, e na quarta parte, o fenômeno da indeterminação na contração muscular. Na quinta parte, será discutida a relação entre o hábito autocontrolado do músculo e os três tipos de raciocínio proposto por Peirce: Abdução, Dedução e Indução. O modelo triádico do signo permite-nos observar na conduta muscular uma ampla esfera de atividades racionais, mostrando-nos que o músculo possui as mais elevadas e refinadas propriedades de uma mente que aprende com a experiência. Assim não há motivos suficientemente fortes ou logicamente sustentados para reivindicar qualquer privilégio à racionalidade humana. / Abstract: This contribution proposes an analysis the human skeletal muscle physiology as a sign process, based on Charles S. Peirce's thought. It contributes to understand the psychophysical relations in the human body by considering muscles an including sphere of mental processes. This paper first discusses the nature of muscular conducts. Following Peirce's Objective Idealism, it is argued that muscle contraction is a typically mental process. It is general and eidetic. In the second part, the muscular physiological conduct is discussed as experience based habits, anticipated by Peirce. In the third part, the relation between final and efficient causation in muscular conduct is examined, and in the fourth part, the phenomena of indeterminacy in muscular contraction. It is argued that objective chance is the only responsible for originating spontaneous and original muscular conducts. In a fifth part, one discusses the relation between the acquired auto-controlled muscular habit and the three different types of reasoning proposed by Peirce: Abduction, Deduction and Induction. One concludes raising the hypothesis that the basis of all muscular cell conduct is evolutionary rationality. The triadic model of Sign proposed by Peirce allows us to observe a wider rationality in muscular conduct. It shows us the higher and refined properties of a Mind that learns by experience. / Mestre

Neste trabalho são propostas pequenas alterações nos principais sinais de trânsito ( Parada Obrigatória – PO e Sentido de Circulação da Via – SCV) para melhorar a percepção dos mesmos por parte dos usuários. As alterações propostas são as seguintes: eliminação da orla externa vermelha do sinal de PO, aumento da orla branca do sinal de PO e da orla vermelha do sinal de SCV e emprego de suportes das placas com espessura significativa e coloridos. Além desses, também são parâmetros, dimensão das placas e dos suportes, bem como a cor e o formato do suporte. Para avaliação das diferentes parâmetros foi utilizada a técnica da psicofísica denominada de Método de Ordenação - Rank Order. As principais conclusões do estudo são as seguintes: a eliminação da orla vermelha das placas de PO melhora a percepção do sinal; o aumento da orla branca da placa de PO e da orla vermelha da placa de SCV contribuem para aumentar o impacto visual (os valores indicados situam-se entre 10 e 12,5% da largura da placa); as dimensões indicadas para as placas são de 70 e 80 cm de largura para placa de PO e de 60 e 70cm para placa de SCV. Os suportes devem ter dimensões entre 10 e 15 cm e devem ser pintados nas cores amarela ou vermelha. Uma observação relevante com relação à pesquisa: na definição das cores dos suportes, a questão estética-harmonia dos conjuntos não foi levada em consideração. / In this work there are proposed small alterations in the principal traffic signs (Stop Sign – SS and One Way Sign – OWS) in order to improve the perception of the same by a part of the usuaries. The alterations proposed are: the elimination of the external red border of the SS sign, the enlargement of the white border of the SS sign and of the red border of the OWS sign and the application of colored sign posts with a significant thickness. In addition to these, the signs and posts dimensions are parameters too, as well as the posts colors and shape. For the assessment of the different parameters a psychophysic technique named Rank Order was utilized. The principal conclusions of the study are the following: the elimination of the red border of the SS sign improve the perception of the sign; the enlargement of the white border of the SS and of the red border of the OWS sign contribute to improve the visual impact (the indicated values situate between 10 and 12,5% of the sign width); the indicated dimensions for the sings are 70 and 80cm of its width for the SS sign and 60 and 70cm for the OWS sign. The posts should have its dimensions between 10 and 15cm e should be painted in the yellow or red colors. An relevant observation related to the research: in the definition of the posts colors, the matter esthetics-harmony of the groups was not considered.

Objetivo. Avaliação da visão de cores de dois grupos experimentais: diabéticos tipo 2 (DM2) sem retinopatia (n=32) e, intoxicados por vapor de mercúrio (Hg) (n=18); e seus respectivos grupos controles (n=23; n=18). Foram reconstruídos os espaços de cores dos indivíduos e dos grupos (DM2, Hg e controles) e, a partir dos mesmos, foram avaliadas as compressões nos eixos verde-vermelho (RG) e azul-amarelo (BY). Método. Os testes D-15 e D-15d foram aplicados em seu procedimento tradicional nos grupos experimentais e controles. Em seguida, os testes foram aplicados em procedimento triádico. Nesse procedimento, as peças foram apresentadas em trios e, o sujeito deveria separar a mais distante (‘odd-one-out’). Os resultados obtidos das relações de similaridade e dissimilaridade foram analisados individualmente por um procedimento de escala multidimensional (mds) não-métrica. Os espaços de cores foram reconstruídos para os indivíduos e os grupos e, representados em forma bi-dimensional, onde as dimensões correspondem aos eixos RG e BY dos sistemas de oponência perceptual. Resultados. Comparados aos respectivos grupos controles, o procedimento tradicional do teste D-15d foi diferente significativamente para a média dos olhos do grupo DM2 (p= 0,27) e do grupo Hg (p= 0,0003). As reduções na visão de cores foram predominantes no eixo BY. Para o grupo DM2, foi encontrada uma correlação negativa entre o desempenho nos testes de visão de cores e o tempo de diagnóstico (R= 0,56, p= 0,001). Na reconstrução dos espaços de cores dos grupos experimentais, as perdas se apresentaram em ambos os eixos, RG e BY, classificadas como difusas. A análise quantitativa dos espaços de cores foi obtida pelo cálculo dos resíduos dos eixos RG e BY dos grupos DM2 e Hg em relação aos respectivos grupos controles. Os valores encontrados para a média dos olhos foram 0,18 (RG) e 0,20 (BY) para o grupo DM2 e, 0,10 (RG) e 0,19 (BY) para o grupo Hg. Na comparação dos resultados entre os grupos experimentais, houve uma maior diferença entre os eixos RG e BY para o grupo Hg. Discussão. Os resultados confirmam os achados de perdas difusas na visão de cores de pacientes DM2 sem retinopatia. Os resultados também confirmam as perdas em pacientes intoxicados por vapor de mercúrio com, no mínimo, mais de um ano de afastamento da fonte de intoxicação e, sugerem a não-reversibilidade da visão de cores. Embora o procedimento tradicional tenha apresentado diferença significativa em relação aos controles, seus resultados sugerem perdas no eixo BY enquanto os espaços de cores sugerem perdas também no eixo RG, caracterizando perdas difusas. Conclusão. A reconstrução dos espaços de cores pode, junto à fundoscopia, colaborar no monitoramento da DM2. No caso da intoxicação por mercúrio, os espaços podem complementar os estudos da possível não-reversibilidade da visão de cores e, gerar mais informações para o estabelecimento de índices mais seguros de exposição crônica ao vapor de mercúrio. O procedimento triádico, além de pouco dispendioso, pode ser utilizado para representar a discriminação cromática e sugere ser mais sensível que o procedimento tradicional. / Purpose. Color vision was examined in two groups of patients, one group with diabetes mellitus type 2 (DM2) without retinopathy (n=32) and a second group with chronic exposure to mercury vapour (Hg) (n=18), as well as in the respective age-matched controls (n=23; n=18) in order to reconstruct their color spaces. We assessed the type and degree of distortions of individual and group color spaces. Method. The experimental groups and age-matched controls were tested using the D-15 and the D-15d tests. In addition, subsets of caps from both tests were employed in a triadic procedure. Matrices of inter-cap subjective dissimilarities were estimated from each subject’s ‘odd-one-out’ choices, and processed using non-metric multidimensional scaling (mds). Two-dimensional color spaces, individual and group (DM2; Hg and control groups), were reconstructed with the axes interpreted as the red-green (RG) and blue-yellow (BY) perceptual opponent systems. Results. In the traditional procedure, the patients results were significantly different from the age-matched control groups for the D-15d test for the mean eyes in the DM2 group (p= 0.027) and in the Hg group (p= 0.0003). The losses in the D15d were concentrated in the BY axis. In the color space analysis color configurations for both groups were compressed along both the RG and BY dimensions. These losses are therefore classified as diffuse. For the quantitative analysis, the residuals were calculated in comparison to controls for the group color spaces. Values for the mean eyes were 0.18 (RG) and 0.20 (BY) for DM2 group, and were 0.10 (RG) and 0.19 (BY) for Hg group. Comparing the results between experimental groups, the degree of compression in the Hg group shows a greater difference in the magnitude of losses between the RG and BY dimension. For DM2, there was a negative correlation between the color vision performance and the time of diagnosis (R= 0.56, p= 0.001). Discussion. The present findings are in agreement with earlier studies demonstrating diffuse losses in early stages of DM2. They also confirm that color vision is impaired in patients with long-term vapour mercury intoxication and suggested that Hg intoxication may not be totally reversible. Since the triadic procedure shows losses in both the RG and BY axes while the traditional procedure shows only BY deficiencies, we consider that the triadic procedure is more sensitive. Conclusion. Along with fundoscopy, individual color spaces may serve for monitoring early functional changes in DM2 and thereby to support a treatment strategy. In case of mercury intoxication, the reconstruction of color spaces may contribute to researches in this field in order to evaluate the possible non-reversible intoxication and gives additive data for the necessity to establish more security indices of occupational mercury exposure. The proposed method of testing uses color spaces to represent discrimination, providing an opportunity for more differentiated diagnosis of the type and the severity of color vision loss.

Objetivo. Avaliação da visão de cores de dois grupos experimentais: diabéticos tipo 2 (DM2) sem retinopatia (n=32) e, intoxicados por vapor de mercúrio (Hg) (n=18); e seus respectivos grupos controles (n=23; n=18). Foram reconstruídos os espaços de cores dos indivíduos e dos grupos (DM2, Hg e controles) e, a partir dos mesmos, foram avaliadas as compressões nos eixos verde-vermelho (RG) e azul-amarelo (BY). Método. Os testes D-15 e D-15d foram aplicados em seu procedimento tradicional nos grupos experimentais e controles. Em seguida, os testes foram aplicados em procedimento triádico. Nesse procedimento, as peças foram apresentadas em trios e, o sujeito deveria separar a mais distante (‘odd-one-out’). Os resultados obtidos das relações de similaridade e dissimilaridade foram analisados individualmente por um procedimento de escala multidimensional (mds) não-métrica. Os espaços de cores foram reconstruídos para os indivíduos e os grupos e, representados em forma bi-dimensional, onde as dimensões correspondem aos eixos RG e BY dos sistemas de oponência perceptual. Resultados. Comparados aos respectivos grupos controles, o procedimento tradicional do teste D-15d foi diferente significativamente para a média dos olhos do grupo DM2 (p= 0,27) e do grupo Hg (p= 0,0003). As reduções na visão de cores foram predominantes no eixo BY. Para o grupo DM2, foi encontrada uma correlação negativa entre o desempenho nos testes de visão de cores e o tempo de diagnóstico (R= 0,56, p= 0,001). Na reconstrução dos espaços de cores dos grupos experimentais, as perdas se apresentaram em ambos os eixos, RG e BY, classificadas como difusas. A análise quantitativa dos espaços de cores foi obtida pelo cálculo dos resíduos dos eixos RG e BY dos grupos DM2 e Hg em relação aos respectivos grupos controles. Os valores encontrados para a média dos olhos foram 0,18 (RG) e 0,20 (BY) para o grupo DM2 e, 0,10 (RG) e 0,19 (BY) para o grupo Hg. Na comparação dos resultados entre os grupos experimentais, houve uma maior diferença entre os eixos RG e BY para o grupo Hg. Discussão. Os resultados confirmam os achados de perdas difusas na visão de cores de pacientes DM2 sem retinopatia. Os resultados também confirmam as perdas em pacientes intoxicados por vapor de mercúrio com, no mínimo, mais de um ano de afastamento da fonte de intoxicação e, sugerem a não-reversibilidade da visão de cores. Embora o procedimento tradicional tenha apresentado diferença significativa em relação aos controles, seus resultados sugerem perdas no eixo BY enquanto os espaços de cores sugerem perdas também no eixo RG, caracterizando perdas difusas. Conclusão. A reconstrução dos espaços de cores pode, junto à fundoscopia, colaborar no monitoramento da DM2. No caso da intoxicação por mercúrio, os espaços podem complementar os estudos da possível não-reversibilidade da visão de cores e, gerar mais informações para o estabelecimento de índices mais seguros de exposição crônica ao vapor de mercúrio. O procedimento triádico, além de pouco dispendioso, pode ser utilizado para representar a discriminação cromática e sugere ser mais sensível que o procedimento tradicional. / Purpose. Color vision was examined in two groups of patients, one group with diabetes mellitus type 2 (DM2) without retinopathy (n=32) and a second group with chronic exposure to mercury vapour (Hg) (n=18), as well as in the respective age-matched controls (n=23; n=18) in order to reconstruct their color spaces. We assessed the type and degree of distortions of individual and group color spaces. Method. The experimental groups and age-matched controls were tested using the D-15 and the D-15d tests. In addition, subsets of caps from both tests were employed in a triadic procedure. Matrices of inter-cap subjective dissimilarities were estimated from each subject’s ‘odd-one-out’ choices, and processed using non-metric multidimensional scaling (mds). Two-dimensional color spaces, individual and group (DM2; Hg and control groups), were reconstructed with the axes interpreted as the red-green (RG) and blue-yellow (BY) perceptual opponent systems. Results. In the traditional procedure, the patients results were significantly different from the age-matched control groups for the D-15d test for the mean eyes in the DM2 group (p= 0.027) and in the Hg group (p= 0.0003). The losses in the D15d were concentrated in the BY axis. In the color space analysis color configurations for both groups were compressed along both the RG and BY dimensions. These losses are therefore classified as diffuse. For the quantitative analysis, the residuals were calculated in comparison to controls for the group color spaces. Values for the mean eyes were 0.18 (RG) and 0.20 (BY) for DM2 group, and were 0.10 (RG) and 0.19 (BY) for Hg group. Comparing the results between experimental groups, the degree of compression in the Hg group shows a greater difference in the magnitude of losses between the RG and BY dimension. For DM2, there was a negative correlation between the color vision performance and the time of diagnosis (R= 0.56, p= 0.001). Discussion. The present findings are in agreement with earlier studies demonstrating diffuse losses in early stages of DM2. They also confirm that color vision is impaired in patients with long-term vapour mercury intoxication and suggested that Hg intoxication may not be totally reversible. Since the triadic procedure shows losses in both the RG and BY axes while the traditional procedure shows only BY deficiencies, we consider that the triadic procedure is more sensitive. Conclusion. Along with fundoscopy, individual color spaces may serve for monitoring early functional changes in DM2 and thereby to support a treatment strategy. In case of mercury intoxication, the reconstruction of color spaces may contribute to researches in this field in order to evaluate the possible non-reversible intoxication and gives additive data for the necessity to establish more security indices of occupational mercury exposure. The proposed method of testing uses color spaces to represent discrimination, providing an opportunity for more differentiated diagnosis of the type and the severity of color vision loss.

A total of 9 brushtail possums (Trichosurus vulpecula) were trained to perform a two-manipulanda, conditional discrimination task. The possums learned to press a right lever in the presence of a tone (80 dB(A)) during tone-on trials, and a left lever in the absence of the tone on tone-off trials. Overall sessions of 11 conditions contained tone frequency between 100 Hz and 35 kHz were tested. Each condition contained training and then probe sessions. In training sessions, the possums were presented with tone-on and tone-off trials, pseudo-randomly. Once the possums responded with over 90% accuracy for five consecutive sessions, then probe sessions were introduced. Probe sessions were similar to the training sessions, except that the tone intensity for tone-on trials was reduced by 8 dB(A) across blocks of 20 trials until their response accuracy in a block fall below 60% or reached 24 dB(A). Data were analysed using overall percentages correct and log d analysis. Both measures indicated that overall response accuracy decreased for all possum as tone intensity reduced. Based on these data analyses, threshold values were calculated using the criterions at 75% correct and a log d of 0.48. The threshold values for each possum and across all possums were plotted as a function of the tone frequency to produce an audiogram. A curvilinear regression was fitted for each threshold values. The functions of both measures were very similar. Both audiograms showed that the possums could hear the tones between 100 Hz and 35 kHz, and were most sensitive to tones between 15 and 20 kHz. This experiment involved many difficulties with producing and measuring tones especially outside of human hearing range. Due to these difficulties, several problems and concerns were raised during the experiment, these were discussed in this study and also recommendations for future research were then presented.

The spatial frequency doubling illusion (FDI) occurs when the contrast of a low spatial frequency sinusoidal grating is modulated at high temporal frequencies – its apparent spatial frequency increases. Earlier suggestions were that the FDI is generated by a specific class of retinal ganglion cells, which are preferentially lost in the early stages of glaucoma. Based on this linking theory, frequency doubling perimetry (FDP) was developed and several clinical reports confirmed its high efficiency in diagnosing early glaucomatous vision loss. However, this linking theory is not universally accepted and newer suggestions posit that the illusion arises because of temporal frequency related difficulties in temporal phase encoding ability. This thesis psychophysically examines the spatiotemporal characteristics of both the FDI and temporal phase encoding ability with achromatic and equi-luminant (both red-green (RG) and blue-yellow (BY)) gratings at a range of spatiotemporal parameters including those eliciting the FDI. (For complete abstract open document)